1. Technical Field
This invention generally relates to trommel assemblies, and more particularly to a transportable trommel assembly wherein the infeed conveyor is attached to the trommel assembly and positionable to both transport and lowered operating positions.
2. Background
Trommels, as known in the prior art, are sizing machines which are used to size and segregate aggregate material such as crushed rock, coal or wood chips, and a wide variety of other materials, into different sized groupings. With a trommel, this is accomplished by passing the material to be sized through a rotating cylindrical screen of a particular screen size.
Simple trommels may have only one screen sieve size and accomplish a single sizing operation wherein the aggregate material that is small enough to pass through the screen is collected on to a moving conveyor underneath the rotating screen and conveyed away to one location, while the material that is too large to pass through the screen eventually works its way down to the discharge end of the screen and is deposited either on another discharge conveyor or simply dumped on the ground.
Two stage trommel screens have two separate sieve sizes for the rotating screen, with the smaller sieve size being located at the infeed end of the rotating screen, and a larger sieve sized screen located nearer the discharge end of the rotating screen. With two-stage trommel screen assemblies, fine materials are first collected at the infeed end of the rotating screen and conveyed off to one location. Larger material that will pass through the larger sieve size located at the discharge end of the rotating screen is collected by a second conveyor, and conveyed to a second location, and the material that will not pass through any of the screen is discharged at the end and either conveyed away or dropped on the ground.
In order for a trommel assembly to work, the infeed end of the rotating screen must be elevated so that material that is infed into the infeed end of the rotating trommel screen will, as it is agitated, work its way down parallel to the longitudinal axis of the screen to the discharge end. If the infeed end of the rotating screen was not elevated, the trommel screen would eventually fill with oversized material and cease to function.
In some applications, trommel assemblies can be more or less permanently located on site. Examples would include processing areas at coal mines and rock quarries. In these applications there is typically provided an infeed conveyor which is used to elevate the material to the infeed end of the trommel screen and drop it in. These infeed conveyors can be permanently mounted, and the mined or quarried material is brought to the trommel assembly for sizing and processing.
In other applications, the trommel assemblies must be portable. The reason for this is that there may not be enough material located at the site to be sized at any given time to facilitate continuous operation. Since trommel assemblies are often times large and very expensive pieces of machinery, it is not cost justifiable to leave, in situ, a trommel assembly which will only be operated one or two days a week or month. An example of this type of application is a logging operation where tree stumps and slash from the logging operation are collected and ground into wood chips using a rotating tub grinder, such as that described in U.S. Pat. No. 4,997,135. Once a particular area has been logged and the tree stumps and slash collected from the area, there will be no more material to be ground and removed, and any trommel assembly that has been used to segregate the material into various sizes will have to be moved to the next logging location.
In some logging operations, the ground wood chip material to be segregated by use of the trommel assembly is not generated at a rate sufficient to justify the full-time use of the trommel assembly, and as a result, the trommel assembly is periodically brought to the site, used for a few days, and then moved on to another site. In these situations, transportable trommels can be economically justifiable, since the segregated material can easily be segregated into fine material which is of high economic value and generally used as mulch for gardens and flower beds, and the intermediate size material can be used as a fuel for power generation, or further processed into wood pellets for use in home heating. And finally, the oversized material can be reprocessed through a rotating tub grinder, so that all of the tree stumps and slash from the logging operation can be fully utilized as a value added product in one form or another.
The problem in the prior art is the time it takes to transport the trommel assembly and set it up for use. For example, in use with logging operations to generate segregated, sized wood chip material, the trommel assembly is transported by a convoy of trucks. One truck transports the trommel, the second transports the infeed conveyor, and a third transports a front end loader or other piece of industrial machinery which is used to load the material to be segregated onto the infeed conveyor, and also the segregated, sized material into trucks for transport from the site. If the infeed conveyor is a separate piece of machinery, it must be attached in some form to the trommel assembly, and this process can take several hours, even for a skilled crew. Thus, in the prior art, an operator would need an extra truck to transport the infeed conveyor, and extra time to set up the entire assembly for operation.
A prior art alternative is to eliminate the infeed conveyor altogether, and instead just provide for a permanent, fixed loading chute at the input end of the trommel screen. The problem with this arrangement is that the infeed end of the trommel screen must be elevated in order for the trommel to work effectively. Thus, a prior art infeed chute is generally located twelve to sixteen feet in the air, thus requiring the use of a larger front end loader capable of elevating its dump bucket far into the air. Not only does this increase the machinery requirements by requiring a larger front end loader, but it also reduces the cycle time of the front end loader, since it has to lift the material higher into the air in order to dump it into the infeed end of the trommel screen.
Accordingly, what is needed is a transportable trommel screen assembly where the infeed conveyor is formed as an integral part of the assembly, and positionable to a transport position which is within transportable trailer length restrictions, and can be quickly set up by repositioning it to a lowered operating position, such that there is a lower lift required of the operator of the front end loader or other loading machine.